1. Field of the Invention
The present invention relates to electron beam lithography systems and, in particular, to a multiple beam system with modulated laser illumination.
2. Description of the Related Art
Electron beam lithography systems generally include an electron source and electron optics for accelerating the electrons into an electron beam and focusing the electrons onto a target, thereby exposing a mask (reticle) or wafer. In a conventional electron beam lithography system, a single beam in a single column is used to expose the resist and create the desired pattern.
The throughput of a conventional lithography system is limited by the total beam current: as the total beam current is increased, electronxe2x80x94electron interactions in the beam cause excessive blur, resulting in a degradation of the resolution in the written pattern. Several approaches are known to reduce electronxe2x80x94electron interactions and the associated beam blur. If the total current is distributed evenly among several beams, a reduction of the beam blur in each column results in higher resolution, and if all beams are operated in parallel, the throughput is not compromised. In addition, the clock rate of each individual beamlet is reduced by a factor equal to the number of beamlets, thus reducing the blanking rate for each beamlet significantly. This is impractical for a conventional column due to its overall dimensions and large footprint.
However, in a single electron beam column, the total current can be divided into several beamlets, which also reduces the blur due to electronxe2x80x94electron interactions and therefore allows a higher total beam current. Single beam-beamlet lithography systems are the patterned photocathode approach described in U.S. Pat. No. 5,684,360, xe2x80x9cElectron source utilizing negative electron affinity cathodes with ultrasmall emission areasxe2x80x9d, the gated electron emitter photocathode approach, described in WO9950874A3, or the VCSEL array approach described in co-pending U.S. patent application Ser. No. M-7958).
These and other drawbacks in the prior art are overcome in large part by an electron beam lithography system in accordance with the present invention.
The electron beam lithography system includes a laser for generating a laser beam, and a beam splitter for splitting the laser beam into a plurality of light beams. The intensity of the light beams is individually modulated. The light beams are of sufficient energy such that, when they impinge on a photocathode, electrons are emitted. Modulation of the light beams controls modulation of the resulting electron beams. The electron beams pass through an electron column for focusing and scanning control. Finally, the electron beams are used to write while scanning across a surface, for example, using an interlaced writing strategy.
In one implementation, a high throughput lithography system includes an electron beam column with a photocathode illuminated by an array of individually blanked laser beams in which the intensity of the individual laser beams is modulated or varied by one or more acousto-optical modulators. In particular, an argon-ion laser with a beam splitter and array of acousto-optic modulators in combination with a photocathode and 50 keV electron beam column is employed.